``` fn main() { println!(format!("{}",123)); } ``` When compiled, rustc will prints: ``` macro.c:12:11: 12:17 error: macro undefined: 'format' macro.c:12 println!(format!("{}",123)); ^~~~~~ macro.c:12:11: 12:17 error: macro undefined: 'format' macro.c:12 println!(format!("{}",123)); ^~~~~~ macro.c:12:11: 12:17 error: macro undefined: 'format' macro.c:12 println!(format!("{}",123)); ^~~~~~ macro.c:12:11: 12:17 error: macro undefined: 'format' macro.c:12 println!(format!("{}",123)); ^~~~~~ macro.c:12:11: 12:17 error: macro undefined: 'format' macro.c:12 println!(format!("{}",123)); ............ ```